652
R. H. THOMSON
(81, 89) in vitro. Another related compound found in tobacco leaf is
solanachromene (LXIX) (86), a cyclic isomer of plastoquinone.
Most higher plants examined so far contain coenzyme Q* but it
appears to be absent (or present in a concentration too low to be detectable) from lettuce, carrots, green peas, cabbage, and potatoes, according to Folkers et dl. (82α). However, Lester and Crane (83)
detected coenzyme \Jio in potato tubers, and also in sweet potato roots,
spinach and alfalfa leaves. [Crystalline Q 10 has since been isolated from
alfalfa (76a).] They also detected unidentified coenzymes Q in young
corn shoots and roots, cauliflower buds, cotton seed, and wheat germ
oil, but not in olive or linseed oil. According to Folkers the isoprenolog
in wheat germ oil and in corn oil is Q 9 , whereas in soybean oil it
In a detailed study of spinach leaves and corn seedlings, Crane (82)
found that coenzyme Q occurred in both white and green tissues, concentrated in the mitochondria (82). This suggests that coenzyme Q is
involved in mitochondrial electron transport in plants, as in animals. In
keeping with the respiratory function of these quinones is the recent
identification of ubiquinone* in the highly aerobic spadix of Arum
maculata Linn. (90).
b. Gymnospermae. In addition to the many terpenes that occur in
the Cupressaceae there are a number of aromatic compounds, including
two quinones,f which are closely related to the monocyclic monoterpenes. Thus Grimal (91) found carvacrol (LXX), thymoquinol and
thymoquinone (LXXII), in the heartwOod of Tetraclinis articulata
(Vahl) Masters, and Zavarin and Anderson (92-94) have isolated the
following compounds from the wood of the incense cedar, Libocedrus
decurrens Torrey: carvacrol, thymoquinol and both its monomethyl
ethers—p-methoxy carvacrol and p-methoxythymol (LXXI)—thymoquinone, libocedrol (LXXIII), heyderiolf (LXV), and 3-libocedroxythymoquinone (LXXIV). Thymoquinone and the monocyclic phenols
have fungicidal properties, which are no doubt partly responsible for
the decay resistance of the heartwoods.
In the laboratory, libocedrol can be prepared by oxidation of
p-methoxythymol with alkaline ferricyanide (94) and both libocedrol
and heyderiol are formed by a similar oxidation of a mixture of pmethoxythymol and p-methoxycarvacrol (93). Zavarin (93) has also
* Further discussion of these compounds, and their formulas, are given on
page 692.
f Now four: 3-hydroxy-, and 3,6-dihydroxythymoquinone have recently been
isolated from the heartwood of Juniperus chinensis
(90a).
% According to Li (95), L. decurrens Torrey is now Heyderia decurrens Torrey.
R. H. THOMSON
(81, 89) in vitro. Another related compound found in tobacco leaf is
solanachromene (LXIX) (86), a cyclic isomer of plastoquinone.
Most higher plants examined so far contain coenzyme Q* but it
appears to be absent (or present in a concentration too low to be detectable) from lettuce, carrots, green peas, cabbage, and potatoes, according to Folkers et dl. (82α). However, Lester and Crane (83)
detected coenzyme \Jio in potato tubers, and also in sweet potato roots,
spinach and alfalfa leaves. [Crystalline Q 10 has since been isolated from
alfalfa (76a).] They also detected unidentified coenzymes Q in young
corn shoots and roots, cauliflower buds, cotton seed, and wheat germ
oil, but not in olive or linseed oil. According to Folkers the isoprenolog
in wheat germ oil and in corn oil is Q 9 , whereas in soybean oil it
In a detailed study of spinach leaves and corn seedlings, Crane (82)
found that coenzyme Q occurred in both white and green tissues, concentrated in the mitochondria (82). This suggests that coenzyme Q is
involved in mitochondrial electron transport in plants, as in animals. In
keeping with the respiratory function of these quinones is the recent
identification of ubiquinone* in the highly aerobic spadix of Arum
maculata Linn. (90).
b. Gymnospermae. In addition to the many terpenes that occur in
the Cupressaceae there are a number of aromatic compounds, including
two quinones,f which are closely related to the monocyclic monoterpenes. Thus Grimal (91) found carvacrol (LXX), thymoquinol and
thymoquinone (LXXII), in the heartwOod of Tetraclinis articulata
(Vahl) Masters, and Zavarin and Anderson (92-94) have isolated the
following compounds from the wood of the incense cedar, Libocedrus
decurrens Torrey: carvacrol, thymoquinol and both its monomethyl
ethers—p-methoxy carvacrol and p-methoxythymol (LXXI)—thymoquinone, libocedrol (LXXIII), heyderiolf (LXV), and 3-libocedroxythymoquinone (LXXIV). Thymoquinone and the monocyclic phenols
have fungicidal properties, which are no doubt partly responsible for
the decay resistance of the heartwoods.
In the laboratory, libocedrol can be prepared by oxidation of
p-methoxythymol with alkaline ferricyanide (94) and both libocedrol
and heyderiol are formed by a similar oxidation of a mixture of pmethoxythymol and p-methoxycarvacrol (93). Zavarin (93) has also
* Further discussion of these compounds, and their formulas, are given on
page 692.
f Now four: 3-hydroxy-, and 3,6-dihydroxythymoquinone have recently been
isolated from the heartwood of Juniperus chinensis
(90a).
% According to Li (95), L. decurrens Torrey is now Heyderia decurrens Torrey.